Coking process



Dec' 26, 1944- w. F. ROLLMAN 2,366,055

COKING PROCESS Filed Feb. 1a, 1941 cox/wc ZONE if mail: A TER nzynvc Dnu coMBas non zo NE products including coke.

Patented Dee. 26, 1944 como PRocEss l Walter F. Rollman, Cranford, N.J., assigner to Standard Oil Develo ration of Delaware pment Company, acorpo- Appucauon February 1s, 1941,'seria1No. 379,397

' (ci. 2oz-s) 7 claims.

The present invention relates to improvements in the art of treatinghydrocarbon oils and, more particularly it relates to a method of cokingheavyl residual petroleum oils, such as topped or reduced crude.petroleum oils, to secure quantities of hydrocarbons boiling within thegas oil range, to-

' gether with some gasoline, normally gaseous 'hydrocarbons and coke.

A great deal of research and experimentation has been carried out by theoil industry directed toward improving coking operations. Heretofore,and in many instances at the present time, after, a crude petroleumoilhas been topped to remove' by distillation constituents boiling up to i.say 825 F.850 F., the residual oil, often called reduced crude, issubjected to a pyrolytic treatment such as coking or viscosity reducingin order' to obtain additional quantities of gas oil, that is,hydrocarbon oils boiling Within the range of say from 400 F.850 F.,which gas oil may be used as a charging stock for a thermal or,preferably,

catalytic cracking operation to produce a gasoline of high octanenumber. In so far as the cokin'g operation is concerned, the practicehas been to preheat the oil to coking temperatures in say a tube furnaceand thereafter to ldischarge the pre- 'heated oil into a coking retortor drum, preferably heat insulated, in which drum the oil undergoesconversion to form gas oil, gasoline and other Insuch an operation, thecoke formed unavoidably deposits as a solid clinging to the bottom andside walls of the drum, which is eventually nearly filled so thatperiodically the operation must be discontinued to remove the coke. Thefirst step in decoking a drum of the kind referred to above is todiscontinue the oil feed and permit the kdrum to stand for a time,

stream operation While the other or others are being decoked.

The Vpresent invention is directed. toward a process for cokingcontinuously and broadly `contemplates so manipulating the coking`operation as to cause the formation of a hard, dry, freeflowing granularcoke which is non-adherentand which therefore may be continuously-removed from the -coking drum thus obviating the necessity ofdiscontinuing the coking operation to remove large quantities of coke. Iaccomplish this result by providing a, coking drum containing threedistinct sections as follows: (1) a topfeed introduction sectionoperating slightly below normal coking temperatures into which sectionthe oil is sprayed; (2) `a 'coking section; and (3) a coke dryingsection maintained at' a, high temperature by the introductiony of` airand fuel gas.

The present invention will be best understood by reference to theaccompanying drawing in which Fig, I shows. schematically a form andarrangement of apparatus elements in which the present invention may -becarried into effect; and

say 24 hours, for the purpose of drying and hardening the containedcoke. At the end of this time hydrocarbon vapors are displaced out ofthe coking drum by means of steam, the drum is cooled with water,opened, and the coke removed. There are'several methods in use for theremoval of coke from the coking drum, namely, pulling out a cable whichwas strung spider-web fashionv in the drum `prior to thel operation;drilling and knocking out the coke with a kind of revolving hammer;l orremoving the coke by means of very high pressure streams Aof wateremitted from a revolving nozzle head pushed t through a hole drilled inthe coke. The decoking of a drum is, therefore, a laborious andtime-consuming opera- Ation when practiced intermittently as indicatedabove. It also requires additional equipment, be-

cause the usual practiceis to employ two or more drums of which ldrumsone or` more is in on- Fig. II shows an Aenlarged modification of theequipment employed in discharging the oil into the coking drum.Throughout the several views similar reference characters refer tosimilar parts.

Referring in detail to the drawing, a heavy hydrocarbon topped crude oilor reduced crude is discharged into the system through line l and thencedischarged into a preheater- 3, and thence discharged through line 5into a coil 6 disposed in a furnace setting 8 where the oil is heated toa temperature of say 800 -F.-950 F. The oil thus heated in coil 6 -isWithdrawn from said coil through line I0 and discharged into a sprayhead I4 located in the upper` section of a vertical coking drum I 6where the oil is formed into small droplets and thereafter dischargedinto the interi`or of said drum. The oil discharged into the drum is ata .temperature such that it will not readily form coke on the inletspray head but isV thereafter heated to coking temperatures in a mannerwhich will be presently explained. The

spray head is, as stated, employed to convert the f y oil stream intoparticles directed straight downwardly, in preference to a nozzle,because of the tendency of a nozzle to. direct some of the oil againstthe wall and to produce some mist; which would entrain out of the drum.The upper or feed zoneis provided with a cooling jacket 20 through whichis circulated water or any other suitable coolant for the purpose ofkeeping this feed zone, and, more particularly, the feed spray head at atemperature slightly Vbelow that at 6 or 8 feet'.

venting the accumulation of coke on the oil feed spray head. Any othersuitable method may be employed to prevent overheating the spray head oroil in contact with it. For example, the inner wall ofy the'feed zonemay be covered with an insulating material to reduce radiation of heatfrom the walls in this section to the spray head: or the feed zone maybe separated from the remainder of the coking drum by means of a heatinsulating gasket to prevent the4 metallic conduction of heat throughthe walls to the feed zone. In any case, the feed zone section need beno longer than is necessary to thus insure that the spray head is notexposed to excessive temperatures. I

The finely divided oil particles fall through a stripping and/or cokingzone S heated to some extent by rising combustion gases formed in amanner which will subsequently be explained., Experience in the study'ofcontinuous coking has shown'that if the oil is preheated substantiallyto coking temperature; and is nely divided, in. a hot coking drumconversion to coke is completed very quickly and consequently the cokingzone need not be excessively long, e. g., it may be say 25 to 100 feet.However, it is not necessary to produce an absolutely dry coke in thecoking zone, and consequently the small quantity of tacky materialremaining after the initial rapid ashing and cracking, which producesvery little useful products and is 'the most `namely, normally gaseoushydrocarbons, and hydrocarbons in the gasoline and gas oil boilingrange, and would also introducev an undesirable quantity of oxygenatedbodies into these products. As a further precaution against gettingexcess oxygen into the coking zone extraneous gas is introduced throughline 35 into perforated ring 36' located at or near the topl of thedrying section, which gas will be consumed by the excess oxygen that mayremain in the drum at this point.V However, it is known that thepresence of some oxygen in the coking drum has l the effect ofincreasing the octane number of the gasoline produced in the'cokingoperation and consequently it Ymay be preferable to perinit some oxygento enter the stripping and coking section, although obviously the amountof 5 d5, thus reducing the quantity of iixedgases refractory fraction ofthe charging material, need not be completelycokedin the coking zone.This is' an important advantage in that it materially shortens thelength of the coking zone required. Oil vapors and some combustion gasesare taken off at. the top of the coking zone through line 26 and thesemay be conducted to fractionating lequipment to separate and recoverdesired fracthe coking Zone through the drying Zone D where they arecompletely dried and, if desired, partially burned to produce heat whichmay be utilized in the operation in section S. The drying zone D vismaintained at a very high temperature, say 1050 F. to 1800 F., by thecornbustion of gas introduced through line 2d vinto a ring burnerSiilocated as shown near the bottom of the drying section, and sincereaction takes place very quicklyat these conditions, this section maybe fairly short, say not more than The air necessary to support thecombustion is introduced through line 32 into a perforated ring member38 similar in construction toring 30. The air and combustion gasdischarged respectively into the coking drum through lines 32 and 28 mayordinarily be at room temperature. A supply of excess air over thatrequired to consume the extraneous combustible gas is discharge throughline 32 into the coking drum, the purpose of the excess 'air being tofacilitate drying by burning off any tacky material which may remain onthe coke particles at this point, and also for the purpose of burningsome of the coke, which thus supplies part of the necessary heat ofcoking.

destroy valuable products of the coking plo'cess,`

which must subsequently be handled by the fractionating equipmentattached to the unitaria also reducing the tendency of oil and cokeparticles to entrain out of the coke drum because of excessive gasvelocities in the stripping and coking section. The sensible heat of thecombustion gases, however, m'ay be used to heat the stripping section ofthe coking drum by passing them through a jacket (not shown) surroundingthis section of the drum, but heat transmission from gases in a jacketof this type to falling particles in the drum is poor, and the slightadvantage ofthe jacket does not usually warrant the expense ofinstalling it. .In any case, much of the sensible heat of the iiue gasesis recovered by heat exchangers with the oil feed by indirect contactand, consequently, only a small fired preheater coil li is required. Ifthe coking process is so operatedthat the flue gases 4g; containhydrocarbons, they may be burned by in- ,5f and'vapor velocities becauseof the comparatively 7 troducing air at or near the point Where thegases enter the heat exchanger 3, that is to say through line 43, andythe sensibleheat thus released rnay be at least in part recovered. inheat exchanger 3. lThe gases passed thru heat exchanger 3 may beWithdrawn from the heat exchanger thru line M Desirable lengths of theseveral sections of the coking drum have been considered above in thediscussion of the respective sections. The relative order of increasingdiameter of the three sections of the coking drum should be, (l) feedsection,

(2) stripping and coking section, and (3) drying section. The feedsection should be as narrow as possible consistent with avoiding thecontact of oil lfeed with the Walls, to prevent hot vapors from thestripping section from sweeping up into the feed section andconsequently overheating and causing the formation of coke onv the feedspray head. The diameter of the stripping and coking section is suchthat the fallingparticles are not likely to deiiect suiciently to comeinto contact with the walls, and vapor velocities are not sufllcient toentrain oil or coke particles out of the drunuyet the diameter of thissection must not be so great thatI vapor contact time and consequentlydestructive cracking in this section is.

excessive. In order to avoid excessive turbulence large volume of.lgases present, the diameter of Some of the hot gaseous prod-" the dryingsection is greater than that, of the stripping and coking section.

and coking of theoil feed. Under the conditions n stated, the cokeformed in the process is in the form of hard, dry pellets or buckshotwhich is free-flowing, and this material collects in the' bottom of thecoking drum ,and may be with;

drawn through star feeder 50 and delivered to storage. Y

Referring in `detail to Figure 11, the spray head consists as shown of aplurality of downwardly.

l projecting nozzles 55 tapering to an'orlce of,

frequent shutdowns to remove coke from the coking drumi. Th'e cokingdrum itself `consists of three sections, namely, a feed section, astripping section, and a coke drying section.l As indicated, the feedstock is discharged into the upper section," namely, the feed section,at a temperature slightly below` normal coking temperatures; and inorder to prevent coking in the feed section, especially on the feedspray head, this section is maintained slightly below coking temperatureby means of water or any other suitable coolant circulated through acooling jacket. The additional heat requiredto cause rapid vand completecoking of the oil particlesis preferably supplied by burning a gas suchas CO, hydrogemjhydrocarbon gases or the like,V in thefdrying section'.It is also preferable to cause some limited combustion of the cokeproduced in the lower part of the stripping section in order to furtherfacilitate drying and coking of the partially coked particles. In somecases it is desirable to maintain an excess of oxygen in the dryingsection and permit part of` it to escape to the coking section, since ithas a stripping and coking section, withdrawing a tacky coke from thesaidy coking and stripping section, and discharging it into a dryingsection Vwhere it is heated by combustion gases to temperaturessuiiiciently high to cause the formation of hard, dry pellets of coke,recovering hydrocarbon vapors from the upper section of the lcoking zoneand pelleted coke from the bottom of the coking section.

2. The process set forth in claim `l in which the oilis preheated to atemperature within the range of from about 800 F. to 950 F., thetemperature in the stripping and coking Irone is from about 850 F. to1200 F., the temperature in the drying zone is from about 1 050 F. to1800 F.,lthe pressure inthe coking drum is from 0 to 100 1bs'./sq;in.gauge'pressure and the feed rate of oil Vtdj-.t-he drum is determined bythe tendency of the-oil or coke particles to be entrained in the vaporsegressing from the coking zone.

3. The.. process set forth in claim l in which the oil is-preheated to.about 825 F., the tem- 4 perature in the coking and stripping zone isabout 1000 F., the temperature inthe drying zone is about o1400 F., thepressure in the coking zone is about 5 Ibis/sq. in. gauge and the feedrate of oil to the coking zone is about 0.6 volume of cold oil per zone`volume per hour.

4. The process set forth in claim 1 in which -the drying sectionis`heated by means of com- I oil-,'-a vertical shell having a feed inletzone, a

' coking'- zone, and `a coke-'gdrying zone, cooling meansin. said feedinletzone, means in said coking zonefor removing oil va'pors. means inthe bottom of said drying z/one for introducing a hot f inert gasthereinto, means in the top of said in said head for introducing oil tobe coked, coolbeen found that'smaltquantities -of oxygen in the cokingzone improve the octane level of the gasoline produced. l j

As for a range of conditions, the charging oil in' line I0 should be ata temperature of from 800 F.950 F. and discharged into the feed sectionat-` this temperature. The pressure maintained in the drum "shouldV` befrom atmospheric to 100 lbs/sq. in. gauge. The temperature in the dryingsection should be from 1050 F.1800 F. for best results. Oil feed rate islimited only by the-tendency of oil to entrain out of the coking drum ordeflect to the sides.v l

Many modifications of my invention may be made without departing fromthe spirit thereof. `WhatI claim is: l l

1. A continuous process for coking heavy resdual hydrocarbon oils whichcomprises prevheating the oil to coking temperatures, atomiz- .ing thepreheated oil into an-elongated vertical coking zone, cooling said oilduring said atomii zation to prevent premature coking, permitting theatomized oil soI formed to descend through ing means adjacent saidoil-introducing means, means in said drying and combustion zone forpassing a current of hot gas upwardly through saidshell, means in saidcollector ring for removing'most of said gases being passed through saidshaft, means near the top of lsaid shell for with-` drawing oil vaporsvand the remainder of said gases. passing upwardly through said shell,and means in thelbottoin of said shell ,for removing '7. A coking towerfor residual oils comprising v'a vertical tubularshell having a head atits upper end and an expanded section near the middle portion thereof,means in said headfor introducing the oil to be coked,V cooling meansadja-l panded section for removing most of said hot gases, and means inthe lower portion of said shell for burning a portion of the coke formedso as to dry the remainder of said coke, and means for withdrawing Idrycoke from the bottom of said shell.

WALTER?. ROLLIIIIAN.v

